Process for producing aldehydes

ABSTRACT

The hydroformylation of olefins and olefinically unsaturated compounds in the presence of a water-soluble rhodium complex compound which contains, as a ligand, at least one sulfonated diphosphine, and a catalyst therefor.

This Application claims the priority of German Application P 40 40315.7, filed Dec. 17, 1990.

The present invention relates to a process for producing aldehydes byhydroformylation of olefins in the presence of water-soluble rhodiumcomplex catalysts.

BACKGROUND OF THE INVENTION

It is known to produce aldehydes and alcohols, which contain one carbonatom more than the starting olefin, by reacting olefins with carbonmonoxide and hydrogen (hydroformylation). The reaction is catalyzed byhydrido-metal carbonyls, preferably those of the metals of Group VIII ofthe Periodic Table (IUPAC Version). Apart from cobalt, which is widelyused industrially as a catalyst metal, rhodium has recently been gainingincreasing importance. In contrast to cobalt, rhodium allows thereaction to be carried out at a low pressure; furthermore,preferentially straight-chain n-aldehydes are formed, with an only minorfraction of iso-aldehydes. Finally, the hydrogenation of the olefins togive saturated hydrocarbons in the presence of rhodium catalysts is alsomarkedly less extensive than with cobalt catalysts.

In the processes accepted in industry, the rhodium catalyst is employedin the form of modified hydrido-rhodium carbonyls which containadditional ligands, especially tertiary organic phosphines orphosphites. In most cases, there is an excess of the ligands, so thatthe catalyst system is composed of the complex compound and free ligand.The use of the rhodium catalysts described allows the hydroformylationreaction to be carried out at pressures below 30 MPa.

In this process, however, it is difficult to separate the reactionproducts and to recover the catalysts which are homogeneously dissolvedin the reaction product. In general, the reaction product is distilledfor this purpose out of the reaction mixture. In practice, however,because of the thermal sensitivity of the aldehydes and alcohols formed,this approach is feasible only in the hydroformylation of the lowerolefins, i.e. olefins having up to about 8 carbon atoms in the molecule.In addition, it has been found that thermal stress on the distillationmaterial also leads to considerable catalyst losses due to decompositionof the rhodium complex compounds.

The drawbacks described are avoided by the use of catalyst systems whichare soluble in water. Such catalysts have been described, for example,in German Patent 26 27 354. The solubility of the rhodium complexcompounds is achieved by the use of sulfonated triaryl-phosphines as acomplexing constituent. In this process variant, the catalyst isseparated from the reaction product after completion of the reaction,simply by separating the aqueous and organic phase; i.e. withoutdistillation and hence without additional thermal process steps. Afurther feature of this procedure is that the n-aldehydes are formedwith high selectivity from terminal olefins, with only very minorquantities of isoaldehyes. Sulfonated triarylphosphines and, inaddition, carboxylated triarylphosphines are preferably used ascomplexing constituents of water-soluble rhodium complex compounds.

The known two-phase processes have proven to be highly suitable on anindustrial scale. Nevertheless, efforts are being made to perfect theprocess even further. Thus, the prior art attempted to increase theactivity of the catalysts by modification of the complex ligands and toextend their activity to further reduce the specific catalystrequirement--both rhodium and ligand--and hence the production costs.Economic factors are also the reason for working towards a markedreduction in the phosphine/rhodium ratio. A further improvement in thehitherto achieved high selectivity with respect to the formation ofnon-branched aldehydes is also desired. Several million tons ofhydroformylation products are manufactured per year, so that even asmall increase in the selectivity has economically significantconsequences.

It is the object of the invention to improve the hydroformylationprocess as outlined above, i.e. to develop catalysts which exceed theactivity and selectivity of known catalysts at a lower possibleligand/rhodium ratio.

SUMMARY OF THE INVENTION

The invention comprises a process for producing aldehydes by reactingmonoolefins, unconjugated polyolefins, cycloolefins, or derivativesthereof with carbon monoxide and hydrogen at temperatures of 20° C. to150° C. and pressures of 0.1 to 20 MPa. The reaction is carried out inthe presence of water-soluble rhodium compounds, containing phosphinesin complex bonding, as catalysts. The process comprises using, as thephosphines, biaryl derived diphosphines of Formula I ##STR1## which aresubstituted by one or more sulfonic acid groups. The A radicals beingindependently alkyl, cycloalkyl, phenyl, tolyl, or naphthyl; the R¹radicals being independently hydrogen, alkyl having 1 to 14 carbonatoms, alkoxy 1 having to 14 carbon atoms, cycloalkyl having 6 to 14carbon atoms, aryl having 6 to 14 carbon atoms, aryloxy having 6 to 14carbon atoms, or a fused benzene ring; the m's being independentlyintegers from 0 to 5 and the n's being independently integers from 0 to4.

The water-soluble rhodium/diphosphine complex compounds used ascatalysts according to the novel process are distinguished by aremarkably high effectiveness, determined by the two criteria of"activity" A, namely ##EQU1## and "productivity" P, namely ##EQU2##

The prior art values of these two parameters, are considerably exceededby the procedure according to the invention. The formation of normalaldehydes increases further and the discharge of rare metal andphosphine with the reaction product is reduced. In addition, theseresults are achieved by the use of catalysts which have a markedly lowerligand/rhodium ratio than those used hitherto. These and other results,which are very valuable for carrying out the process on an industrialscale, were neither derivable from theoretical considerations norforeseeable from experience in practice.

DETAILED DESCRIPTION OF THE INVENTION

The sulfonated diphosphines used as the catalyst constituent for thenovel process can be prepared from biaryls, which are available by knownsyntheses, for example by coupling aryl-Grignard reagents with arylhalides. The introduction of the phosphorus-organic radical--(H₂ C)_(m)P(A)₂ --into the biaryl molecule is also carried out by conventionalmethods, for example by reacting a phosphorus compound of the generalformula X--(H₂ C)_(m) P(A)₂, in which X is a halogen atom, with thebiaryl in the presence of a reagent which eliminates protons, such assodium amide or butyllithium. In the last reaction step, the diphosphineis sulfonated with oleum, i.e. with a solution of sulfur trioxide insulfuric acid, at temperatures of 0° C. to 60° C. The sulfonationproduct is isolated from the acidic solution, and diluted with water inaccordance with the state of the art, for example by extraction with thesolution of a water-insoluble amine in a water-insoluble organicsolvent.

Preferred sulfonated diphosphines in the procedure according to theinvention are those which are derived from biaryls of the generalformula I, in which the A radicals are independently phenyl, tolyl, ornaphthyl; the R¹ radicals are independently hydrogen, methyl, isopropyl,isobutyl, t-butyl, phenyl, naphthyl, or a fused benzene ring (so that anaphthyl structure is formed), m is 1, and n is 0 or 1.

Sulfonated diphosphines whose biaryl skeleton is substituted by radicalsR¹ in the 6- and 6'-positions are also of great importance in theclaimed process. The presence of these radicals hinders the rotation ofthe two substituted phenyl radicals. Rhodium complex compounds whichcontain such molecules as ligands can therefore be used as catalysts forenantioselective reactions.

Examples of diphosphines which are successfully used in the novelprocess are the products obtained by sulfonation of2,2'-bis(diphenylphosphanomethyl)-biphenyl (hereinafter BISBIS) and ofthe2-(diphenylphosphanomethyl)-1-[2-(diphenylphosphanomethyl)phenyl]-naphthalene(hereinafter PHENAPS).

It is not necessary to use the disphosphines as single compounds.Mixtures of sulfonated disphosphines derived from biaryl compounds ofdifferent structure are also suitable as are mixtures of biarylscontaining identical or different phosphine radicals and havingdifferent degrees of sulfonation. Finally, mixtures of sulfonated mono-and di-phosphines in combination with rhodium also give very activecatalysts. Thus, for example, mixtures of BISBIS and Natriphenylphosphine-trisulfonate (called TPPTS below) have proven quitesuitable.

It has also been found advantageous to use rhodium and sulfonateddiphosphine not in the stoichiometric ratio, i.e. not corresponding tothe chemical composition of the rhodium complex compound which forms inthe course of the hydroformylation reaction, but to employ an excess ofdiphosphine. The rhodium/diphosphine ratio can here be varied withinwide limits, and about 1 to 130 mol of diphosphine can be used per molof rhodium. A rhodium/diphosphine molar ratio of 1:2 to 1:25 andespecially 1:2 to 1:10 is preferred.

Rhodium is employed either as the metal or as a compound. In themetallic form, it is used either as finely dispersed particles or it isprecipitated as a thin coating on a support such as activated carbon,calcium carbonate, aluminum silicate, or alumina. Suitable rhodiumcompounds are substances which are water-soluble or become water-solubleunder the reaction conditions. The various rhodium oxides, salts ofinorganic hydrogen acids, salts of oxygen acids, salts of aliphaticmonocarboxylic acids, and salts of polycarboxylic acids are suitable.Examples of rhodium salts are rhodium nitrate, rhodium sulfate, rhodiumacetate, rhodium 2-ethylhexanoate, and rhodium malonate. Rhodium halogencompounds are, however, less suitable because of the corrosive behaviorof the halide ions. In addition, rhodium carbonyl compounds such as Rh₃(CO)₁₂, Rh₆ (CO)₁₆, or complex salts of rhodium, e.g.cyclooctadienyl-rhodium compounds, can also be used. Rhodium oxide, andespecially rhodium acetate and rhodium 2-ethylhexanoate are preferred.It must be assured that, in the presence of water gas, water-solublerhodium complex compounds which contain carbon monoxide and diphosphineas ligands are formed under the conditions of the hydroformylationreaction. Together with the diphosphine dissolved in the water, theyconstitute the catalyst system.

The catalyst solution may be prepared from the components either in thehydroformylation reactor, or beforehand in separate equipment and thenfed to the hydroformylation reactor. The concentration of rhodium in theaqueous catalyst solution is 20 to 1000 ppm by weight (based on thesolution), preferably 100 to 600 ppm by weight, and most preferably 200to 400 ppm by weight.

The reaction of the olefin with carbon monoxide and hydrogen takes placeunder pressures from about 0.1 to about 30 MPa, preferably about 1 toabout 12 MPa, and most preferably about 3 to about 7 MPa. Thecomposition of the synthesis gas, i.e. the volume ratio of carbonmonoxide and hydrogen, can extend over wide ranges and be varied, forexample, between 1:10 and 10:1. In general, gas mixtures are used inwhich the volume ratio of carbon monoxide and hydrogen is about 1:1 ordeviates only slightly from this value in either direction. The reactiontemperature is between about 20° C. and 150° C., preferably 80° C. to140° C., and most preferably 100° C. to 125° C. are preferred.

The conversion of the reactants present in the liquid and gaseous phasestakes place in conventional reactors. The progress of the reaction isdecisively influenced by the fact that the aqueous catalyst solutionmust be saturated with the liquid or gaseous hydrophobic olefin and withthe synthesis gas. It is therefore necessary to produce the greatestpossible contact area between the phases. It has proven suitable to stirthe liquid reactor contents (catalyst solution, if appropriate liquidolefin, and reaction product) intensively and to feed the gaseousreactants (synthesis gas and, if appropriate, olefin) to the liquidphase via distribution devices. It has been found to be very desirableto minimize the fraction of the organic phase in the reaction mixture.Surprisingly, the organic phase does not contribute to the solubility ofthe reactants in the aqueous phase, and undesired side reactions of thereaction product, which cannot be excluded in the case of increasingresidence time of the product in the reactor, are avoided. Accordingly,the volume ratio of aqueous phase to organic phase is desirably 1:1 to100:1, preferably 10:1 to 100:1. For this purpose, a corresponding partof the reaction mixture can be discharged continuously from the reactor,the aqueous and organic phases can be separated from one another and theaqueous phase can be recycled to the reactor. The reaction can becarried out batchwise or, preferably, continuously.

The process according to the invention is successfully applicable to theconversion of monoolefins, unconjugated polyolefins, cyclic olefins, andderivatives of these unsaturated compounds. The olefins can be straight-or branched chain, and the double bonds can be terminal or within thechain. Examples of olefins which can be used in the novel process areethylene, propylene, butene-1, butene-2, pentene-1, 2-methyl-butene-1,hexene-1, hexene-2, heptene-1, octene-1, octene-3, 3-ethyl-hexene-1,decene-1, undecene-3, 4,4-dimethyl nonene-1, dicyclopentadiene,vinylcyclohexene, cyclooctadiene, and styrene. Examples of derivativesof the olefins which can be hydroformylated by the claimed procedure,are alcohols, aldehydes, carboxylic acids, esters, nitriles, and halogencompounds. Specifically, allyl alcohol, acrolein, methacrolein,crotonaldehyde, methyl acrylate, ethyl crotonate, diethyl fumarate,diethyl maleate, and acrylonitrile are advantageous. With particularsuccess, the process is employed for the hydroformylation of olefins andolefin derivatives having 2 to 12 carbon atoms.

The examples which follow illustrate the invention, without restrictingit to the embodiments described in detail.

EXAMPLES 1-4

A mixture of equal parts by volume of CO and H is fed into a 0.2 literstainless steel autoclave fitted with a stirrer at a rate such that 10liters (S.T.P.) of exit gas can be taken from the reactor per hour. Atthe same time, 300 ml of aqueous catalyst solution per hour arecirculated through the reactor. The catalyst is composed of 0.09 g ofrhodium (as the acetate) and 5.89 mmol of P(III) (in the form ofBISBIS), which have been dissolved in degassed and nitrogen-saturatedwater to give 300 ml of solution. The phosphorus/rhodium molar ratio is6.7:1, corresponding to a ligand/rhodium ratio of 3.4:1. The reaction ofthe reactants takes place at a temperature of 122° C. and a pressure of5 MPa.

In the table 1 which follows, the results of the process according tothe invention (Examples 1 to 3) are compared with Example 4 which is aprocedure according to the state of the prior art(catalyst:rhodium/TPPTS). Examples 2 and 3 show very clearly that thenovel procedure permits, in a completely surprising manner, aconsiderable increase in the propylene feed rate. Under such reactionconditions, the known processes with Rh/TPPTS catalysts give only verylow conversions or none at all.

                                      TABLE 1                                     __________________________________________________________________________                                          Example 4                               Experimental conditions                                                                           Example 1                                                                           Example 2                                                                           Example 3                                                                           (comparison)                            __________________________________________________________________________    Catalyst            Rh/BISBIS                                                                           Rh/BISBIS                                                                           Rh/BISBIS                                                                           Rh/TPPTS                                Rhodium/ligand      1:3.4 1:3.4 1:3.4 1:80                                    (mol/mol)                                                                     Temperature (°C.)                                                                          122   123.5 122   122                                     Pressure (MPa)      5.0   5.0   5.0   5.0                                     Propylene feed rate (g/h)                                                                         39.0  91.6  110.6 37.6                                    Experimental results                                                          Conversion (%)      79.9  57.8  47.9  41.8                                     ##STR2##           30.25 60.5  90.4  15.8                                     ##STR3##           0.412 0.824 1.16  0.213                                   n-Aldehyde (g/h)    49.2  98.2  90.8  28.0                                    n/i ratio (parts by weight)                                                                       97/3  97/3  96/4  94/6                                    Alcohol (%)         8.45  1.34  2.07  0.73                                    Others (%)          1.5   0.16  0.24  0.57                                    __________________________________________________________________________

While only a limited number of specific embodiments have been expresslydisclosed, it is, nonetheless, to be broadly construed, and not to belimited except by the character of the claims appended hereto.

EXAMPLES 5-14

Examples 5 to 14 relate to the hydroformylation of propylene in theapparatus used in the Examples 1 to 4. The reaction conditions aresummarized below, the results of the experiments are summarized in Table2.

    ______________________________________                                        Reaction conditions                                                           ______________________________________                                        Catalyst            Rh/BISBIS                                                 Rh concentration (ppm, based                                                                      306                                                       on the catalyst solution)                                                     Rh/ligand (mol/mol) 1:3.4                                                     Temperature (°C.)                                                                          125                                                       Pressure (MPa)       5                                                        ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________                        Examples                                                                      5  6  7  8  9   10  11  12  13  14                        __________________________________________________________________________    Propylene feed rate (g/h)                                                                         23.0                                                                             49.9                                                                             65.9                                                                             82.7                                                                             100.8                                                                             110.6                                                                             128.4                                                                             125.2                                                                             124.0                                                                             108.0                      ##STR4##           27.45                                                                            42.4                                                                             54.58                                                                            67.37                                                                            64.37                                                                             90.47                                                                             90.31                                                                             46.29                                                                             31.04                                                                             97.68                      ##STR5##           0.35                                                                             0.55                                                                             0.70                                                                             0.87                                                                             0.83                                                                              1.16                                                                              1.16                                                                              0.60                                                                              0.40                                                                              1.26                      n-Aldehyde (g/h)    83.48                                                                            84.59                                                                            85.46                                                                            87.58                                                                            89.73                                                                             87.64                                                                             88.0                                                                              89.35                                                                             89.00                                                                             87.37                     n/i ratio (parts by weight)                                                                       95.61                                                                            97.05                                                                            96.12                                                                            95.81                                                                            95.89                                                                             95.72                                                                             92.26                                                                             96.45                                                                             96.51                                                                             96.86                     Alcohol (parts by weight)                                                                         9.82                                                                             9.25                                                                             6.12                                                                             3.36                                                                             2.13                                                                              2.37                                                                              1.85                                                                              1.70                                                                              1.72                                                                              1.37                      __________________________________________________________________________

EXAMPLES 15-19

Examples 15 to 19 relate to the hydroformylation of hexene in theapparatus used in Examples 15 to 19. the reaction conditions aresummarized below, the results of the experiments are summarized in Table3.

    ______________________________________                                        Reaction conditions                                                           ______________________________________                                        Catalyst            Rh/BISBIS                                                 Rh concentration (ppm, based                                                                      306                                                       on the catalyst solution)                                                     Rh/ligand (mol/mol) 1:3.4                                                     Pressure (MPa)       5                                                        ______________________________________                                    

                                      TABLE 3                                     __________________________________________________________________________                        Examples                                                                      15  16  17  18  19                                        __________________________________________________________________________    Hexene feed rate (g/h)                                                                            14.50                                                                             13.90                                                                             13.90                                                                             15.50                                                                             15.40                                      ##STR6##           0.73                                                                              1.27                                                                              1.99                                                                              4.16                                                                              10.69                                      ##STR7##           0.004                                                                             0.007                                                                             0.011                                                                             0.023                                                                             0.058                                     n-Aldehyde (g/h)    4.60                                                                              8.90                                                                              13.80                                                                             26.10                                                                             30.30                                     n/i ratio (parts by weight)                                                                       97.12                                                                             96.23                                                                             96.00                                                                             95.38                                                                             94.56                                     __________________________________________________________________________

What we claim is:
 1. A catalyst for hydroformylation of a monomerselected from the group consisting of monoolefins, unconjugatedpolyolefins, cycloolefins, and derivatives thereof, said catalystcontaining rhodium and a diphosphine, said diphosphine resulting fromsulfonation of biaryl compounds of Formula I ##STR8## wherein the Aradicals are independently alkyl, cycloalkyl, phenyl, tolyl, ornaphthyl; the R¹ radicals are independently hydrogen, alkyl having 1 to14 carbon atoms, alkoxy having 1 to 14 carbon atoms, aryloxy having 1 to14 carbon atoms, cycloalkyl having 6 to 14 carbon atoms, aryl having 6to 14 carbon atoms, aryloxy having 6 to 14 carbon atoms, or a fusedbenzene ring; the m's are independently integers from 0 to 5, and then's are independently integers from 0 to
 4. 2. The catalyst of claim 1wherein said rhodium and said diphosphine are present in a molar ratioof 2:1 to 1:2.